Fix collation of JSON_TABLE output columns

The output columns of JSON_TABLE should have the collations of their
data type.  The existing implementation sets the default collation if
the type is collatable.

Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Discussion: https://www.postgresql.org/message-id/flat/9d75ce67-0121-5050-5bec-bf5009db55ce%40enterprisedb.com

src/backend/parser/parse_jsontable.c

@@ -514,10 +514,7 @@ appendJsonTableColumns(JsonTableContext *cxt, List *columns)
 
 		tf->coltypes = lappend_oid(tf->coltypes, typid);
 		tf->coltypmods = lappend_int(tf->coltypmods, typmod);
-		tf->colcollations = lappend_oid(tf->colcollations,
-										type_is_collatable(typid)
-										? DEFAULT_COLLATION_OID
-										: InvalidOid);
+		tf->colcollations = lappend_oid(tf->colcollations, get_typcollation(typid));
 		tf->colvalexprs = lappend(tf->colvalexprs, colexpr);
 	}
 }